In the field of medical examinations, such as in a computerized tomography (CT) or nuclear magnetic resonance (MR) examination, a scan range normally needs to be determined. This can be achieved by acquiring a scout image of the object to be scanned and providing a suitable localizer therein. However, the current provision of a localizer is essentially achieved by manual operations of an operator, which is not only laborious and time-consuming, but also difficult to ensure precision of the location and angle of the localizer, such that it is difficult to obtain an accurate scan range.
The following takes a complete head CT scan as an example to illustrate the existing workflows.
For a complete head CT scan, current workflows are mainly dependent upon manual operations, as is illustrated in FIG. 1. At step S110, the patient is positioned on the table. At step S120, the table is manually adjusted so as to enable the laser line to cross the head of the patient, and the head pose of the patient is also manually adjusted such that the orbitomeatal baseline (OMBL) of the patient fits the laser line, or the CT gantry is manually tilted such that the laser line fits the OMBL of the patient. Be it manually adjusting the head pose of the patient so as to enable the OMBL of the patient to fit the laser line, or manually tilting the CT gantry so as to enable the laser line to fit the OMBL of the patient, said manual operation is not only laborious and time consuming, but also difficult to fulfill an accurate OMBL alignment. Therefore, repeated adjustment may be needed. This manual operation is generally called “pose adjusting”.
After pose adjustment, a scout scan will be performed as shown by step S130, where the scan range of the scout scan is estimated. The scan range should at least cover the entire head range. After a scout image is acquired, at step S140, the user needs to manually adjust the location and angle of the OMBL based on the scout image. To be specific, the user clicks or drags the mouse to change the start location, end location, and angle of a scan group, and adjusts the scan width according to the head image. This manual operation is generally called “localizer adjusting”.
If the patient's head moves after the pose adjustment but before the scout scan, the user needs to re-set the tilt angle of the CT gantry, or re-adjust the head pose of the patient.
At step S150, the user manually sets a scan range. FIG. 3 shows schematically a scan range. As shown in FIG. 3, the length of the scan range is from the OMBL denoted by broken lines on the right side to the head vertex denoted by broken lines on the left side, and the width thereof is the head width parallel to the OMBL.
After all key parameters (e.g., the location and angle of the OMBL, and the scan range) become proper, the head is scanned (e.g., an axial scan or a helical scan), as shown at step S160.
Current typical workflows for a complete head CT scan are subject to the following problems: manual alignment of the laser line or the scan plane to the OMBL is laborious and time consuming; manual alignment of the laser line or the scan plane to the OMBL may be inaccurate if the operator is not familiar with the operation; the OMBL angle is sometimes too inclined to the eyes, resulting in an unnecessary part of eyeballs being scanned; and the OMBL angle is sometimes too inclined to the cerebellum or is translated to the cerebellum, resulting in part of the brain tissue being missed, such that a repeated scan or complementary scan may be clinically needed.
Recently, there have been some researches on image registration based methods, which attempt to detect and locate the OMBL automatically. However, image registration is not suitable for indistinct scout images, such as scout images of the head. Scout images such as CT scout images include a huge volume of 3D information overlapped on a 2D plane, possibly lacking sharp and definite edges and outstanding feature points. Therefore, up to now, there is no appropriate image registration method successfully applicable to automatic detection and location of the OMBL in CT scout images.
Therefore, a method and system for automatically determining a localizer in scout images is needed.